I’m still not sure about Three for roaming. It works… to a point and there’s more destinations included than just the EU, but I’ve always found it disappointing.
I’ve just come back from two weeks in Poland where while I was in Kraków everything was fine - but out in the sticks, where they rely on the smaller of the networks, ‘Play’, then things got tricky. Voice and SMS were mostly there or there abouts… but data was just plain unreliable.
I give up on three by the end of week one and dug out my old Polish SIM card from before free EU roaming was a thing - ironically on ‘Play’, who, for their own customers have internal roaming agreements so you can use T-Mobile or Orange when there’s no native Play available.
Three didn’t work well for me in Las Vegas or San Francisco - though this was a couple of years ago when Roam like Home was new. Again it was the data.
I’ve ended up buying an Orange SIM in Spain because Three was just shite.
About the only place where things went well for Three was my stag do in Czechia earlier this summer.